Abstract

Nymphs of the pomelo psyllid, Cacopsylla (Psylla) citrisuga Yang & Li, were collected from huanglongbing (HLB) symptomatic lemon trees, Citrus limon (L.) in Yunnan Province, China. DNA samples extracted from groups of 2-10 pomelo psyllid nymphs of all stages and from leaves of lemon plants were analyzed with nested-PCR in order to detect ‘Candidatus Liberibacter asiaticus’ (Las). The results showed that 24 out of the 49 lemon trees were Las-positive. Also psyllid nymphs collected from 10 out of the 24 Las-positive plants were Las-positive. DNA extracted from individual late stage nymphs (3rd to 5th instars) collected from Las-infected trees were then subjected to nested-PCR trials. Twelve out of the 29 nymphs proved to be Las positive. All nymphs collected from Las-negative lemon trees were also Las-negative. Most psyllid samples which showed positive in nested-PCR were also positive in conventional-PCR detection. The amplified fragment of the 16S rRNA gene of ‘Ca. Liberibacter spp.’ from positive psyllid samples was 99% similar to those of Las strain psy62 in GenBank. These results demonstrate that Cacopsylla (Psylla) citrisuga is another Las carrier insect. Transmission studies are underway to determine whether Las-positive psyllids can transmit Las to healthy citrus.